1. Field of the Invention
The present invention relates to a sheet transport apparatus, which transports a sheet, and an image forming apparatus that uses the sheet transport apparatus.
2. Related Background Art
Conventionally, there have been used electrophotographic image forming apparatuses, such as copying machines, printers, and facsimiles, which form an image on a first surface of a sheet and then form an image on a second surface of the sheet on an opposite side using an image forming portion, for instance. In such an image forming apparatus that forms images on both surfaces of a sheet in this manner, after a toner image formed on a photosensitive drum is transferred onto a first surface of the sheet, the transferred toner image is heated and pressurized by a fixing means for fixation. Following this, the sheet is sent to an image forming portion again through a re-transport path and a toner image is transferred onto a second surface of the sheet and is fixed by the fixing means.
During this operation, it is necessary to heat the sheet for fixing the toner image on the first surface. If the sheet is sent to the image forming portion again and image formation on the second surface of the sheet is performed while the sheet is still heated, it is possible that a defective image may be formed on the second surface due to the influence of the heat of the sheet. In view of this problem, there is adopted a system in which, after the image formation on the first surface, the sheet having the image formed on the first surface is cooled using a fan or the like on the downstream side of the fixing means or in the re-transport path.
However, a control substrate for controlling the image forming portion and a sheet transport portion is also arranged inside the image forming apparatus, and consequently, air heated as a result of the cooling operation, strikes the control substrate and increases the temperatures of elements on the control substrate, which may cause a control failure.
Also, in recent years, the speeding up of the transport process and image forming process of image forming apparatuses results in the increase of the amount of heat generation, and therefore the influence on the control substrate is further increased. Further, if a fan for cooling the control substrate is arranged separately from the fan for cooling the sheet heated as a result of the heating operation in the fixing means, for instance, this results in increases in apparatus size and cost.